The invention relates to an arrangement for transmitting a first information signal over a signal transmission path, the arrangement comprising a transmitter and a receiver, the transmitter comprising means for frequency modulating a carrier signal by the first information signal and means for amplitude limiting the frequency modulated carrier signal so that the information content of the frequency modulated signal is contained solely in the transition times of the frequency modulated carrier signal and the receiver comprising means for demodulating the frequency modulated carrier signal to recover the first information signal. The invention further relates to a transmitter and to a receiver for use in such an arrangement. The invention still further relates to a communication system including such an arrangement.
Such an arrangement is disclosed in U.K. Patent Application No. 2093664 (PHB 32759). The provision of broadband communication networks for business houses or local communities is attracting increasing attention. Until recently networks carrying telephone services were all that existed. Now, digital data services are becoming increasingly common and a variety of local area networks (LAN's) are available. Additionally the public networks are adopting the integrated services digital network (ISDN) concepts, with the introduction of digital switches.
It is likely that in the future there will be a demand for the addition of a full television capability to the local network. Thus, there will be a requirement for the distribution of television signals as well as person to person switched services such as telephone, video phone and data services. The addition of television services will require an increased bandwidth in the transmission links. If a star configuration network is adopted for two-way switched video applications then the links will be required to carry one or more video channels in each direction plus all the data and voice services. The lengths of the transmission links may vary from a few meters for small LANs to several kilometers for local community networks.
Proposals have been made for a fully digital broadband network with bit rates of up to 140 Mbits for the transmission of video signals. The data, voice and video signals would be multiplexed together for transmission over optical fiber to the central switching point. Such a system is expensive to implement since the switching matrix has to operate at clock frequencies of around 140 MHz. Synchronization of the entire network is necessary to implement the multiplexers and demultiplexers and to enable the use of efficient switching networks employing re-arrangeable routing. While it would be possible to implement such arrangements by means of LSI circuits at clock rates of 2 MHz this option is not presently available at clock rates of 140 MHz because of difficulties with power consumption at those frequencies. Consequently a fully digital broadband network with bit rates of 140 Mbit/sec would be expensive to construct with current technology.